Liquid cooled rotor assembly

ABSTRACT

A rotor assembly cooling system ( 100 ) and method of using same are provided. A portion of the rotor shaft ( 103 ) is hollow, the rotor shaft including an open end ( 107 ) and a closed end ( 105 ). A coolant feed tube ( 109 ) is rigidly attached to the rotor shaft ( 103 ) using one or more support members ( 111 ), thus causing the shaft and the feed tube to rotate at the same rate. Coolant is pumped through the feed tube until it exits the end of the feed tube and flows against the inside surface of the closed end of the rotor shaft causing the coolant to change direction and flow back through the coolant flow region, this region being defined as the space between the outer surface of the feed tube and the inner surface of the hollow rotor shaft.

FIELD OF THE INVENTION

The present invention relates generally to electric vehicles and, moreparticularly, to a method and apparatus for efficiently cooling therotor in the drive motor of an electric vehicle.

BACKGROUND OF THE INVENTION

Electric motors can generate considerable heat, thereby making motorcooling difficult, especially in the traction motor of a vehicle wheresize and weight constraints are coupled with the need for high output.Additionally, in order to avoid excessive wear due to differentialthermal expansion, it is important to cool the internal motor components(e.g., rotor) as well as the outer motor components (e.g., casing,stator). Lastly, the means used to cool the motor must not besusceptible to large variations in the operating environment as such amotor can be expected to be subjected to a wide range of ambienttemperatures, humidity levels and dust/dirt levels.

A number of different approaches have been taken to meeting the coolingdemands placed on a vehicle's electric motor. For example, U.S. Pat. No.6,191,511 discloses using a closed loop, liquid cooling circuit to tryand achieve a temperature balance within the motor, the cooling circuitpassing the coolant through both the stator and a hollow rotor shaft.Within the hollow rotor shaft is a stationary injection tube, theinjection tube fixed to the stator flange. The coolant is pumped throughthe injection tube to the end of the rotor shaft where it is driven backbetween the injection tube and the hollow rotor. The coolant then passesthrough a cylindrical cooling chamber extending over the length andperiphery of the stator before cooling the stator structure and beingreturned to the injection tube.

U.S. Pat. No. 6,329,731 discloses a liquid cooled electric motor inwhich one of the main elements of the planetary gear drives thedisplacement pump of the cooling circuit. The coolant is driven througha stationary tube about which the hollow rotor shaft rotates. Thecoolant then passes between the stationary tube and the hollow rotorshaft before passing through a radiator incorporated into the motor andplanetary gear casing.

U.S. Pat. No. 7,156,195 discloses an electric motor in which the liquidcoolant is collected within the reduction gear case, not the motor case,thus avoiding deterioration and alteration of the motor magnets. Thecoolant from the reservoir is pumped through the end of a passage in thedrive shaft where it flows toward the motor. Part of the coolant issprayed onto the reduction gears while the rest of the coolant is pumpedbetween the drive shaft and the reduction gear shaft and the motoroutput shaft.

The present invention provides an improved rotor assembly coolingsystem.

SUMMARY OF THE INVENTION

The present invention provides a rotor assembly cooling system andmethod of using same. A portion of the rotor shaft is hollow, the rotorshaft including an open end and a closed end. A coolant feed tube isrigidly attached to the rotor shaft, the feed tube being mounted withinthe hollow portion of the rotor shaft, thus causing the shaft and thefeed tube to rotate at the same rate. Coolant is pumped through the feedtube until it exits the end of the feed tube and flows against theinside surface of the closed end of the rotor shaft causing the coolantto change direction and flow back through the coolant flow region, thisregion being defined as the space between the outer surface of the feedtube and the inner surface of the hollow rotor shaft.

One or more support members rigidly attach the feed tube to the insidesurface of the hollowed out portion of the rotor shaft. In at least oneembodiment, a plurality of support members is used in which each of thesupport members is comprised of a plurality of spokes. In at least onealternate embodiment, a plurality of support members is used in whicheach of the support members is comprised of a an inner ring attached tothe outer surface of the feed tube, an outer ring attached to the insidesurface of the rotor shaft, and a plurality of spokes coupling the tworings together. In at least one other alternate embodiment, a pluralityof support members is used in which each of the support members iscomprised of a ring, wherein the inner surface of each ring is attachedto the outer surface of the feed tube, the outer surface of each ring isattached to the inside surface of the rotor shaft, and wherein each ringincludes a plurality of holes or slots passing from one side of the ringto the other side of the ring. The holes or slots are either direct orslanted. In at least one other alternate embodiment, the support memberis a continuous support strut that is helically wrapped around andattached to the outer surface of the coolant feed tube, wherein an outeredge of the support structure is proximate to and attached to the innersurface of the rotor shaft.

In at least one embodiment of the invention, the inner surface of theclosed end of the rotor shaft is shaped, thereby promoting thedirectional change of the coolant from a first direction through thefeed tube to a second direction through the coolant flow region betweenthe outer surface of the feed tube and the inner surface of the rotorshaft.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the primary components of therotor assembly cooling system;

FIG. 2 is a cross-sectional view of one embodiment of a feed tubesupport member utilizing a plurality of support spokes;

FIG. 3 is a cross-sectional view of an alternate embodiment of a feedtube support member utilizing a plurality of support spokes coupled to apair of concentric mounting rings;

FIG. 4 is a cross-sectional view of a perforated feed tube supportmember;

FIG. 5 is a cross-sectional view of a slotted feed tube support member;

FIG. 6 is an illustration of an alternate rotor assembly cooling systemusing a helical support strut between the coolant feed tube and the boreof the rotor drive shaft;

FIG. 7 is an illustration of an alternate rotor assembly cooling systemusing an internally shaped drive shaft; and

FIG. 8 is a conceptual illustration of the rotor assembly cooling systemwithin an electric motor system.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

FIG. 1 schematically illustrates the primary components of the rotorassembly cooling system of the invention. Rotor assembly 100 includes arotor 101 fixed to a rotor drive shaft 103. Drive shaft 103 is hollowand closed at end 105 and open at end 107. Although not a requirement ofthe invention, preferably shaft 103 is hollow over the majority of itslength, including that portion of the shaft in contact with rotor 101,thereby insuring efficient cooling of the rotor assembly. A hollowcoolant feed tube 109 is rigidly attached to shaft 103 with at leastone, and preferably a plurality of support members 111.

During operation, coolant is pumped into end 113 of feed tube 109. Thecoolant flows through the length of feed tube 109 until it is redirectedby the inside surface of closed end 105 of shaft 103. The coolant thanflows back along direction 115 towards the inlet, passing within thecoolant flow region between the outer surface of feed tube 109 and theinside surface of shaft 103 thereby cooling the drive shaft and theattached rotor.

As both shaft 103 and feed tube 109 rotate, the assembly requires atleast one coolant seal 117 to seal rotating shaft 103, and at least asecond coolant seal 119 to seal rotating feed tube 109. It will beappreciated that seal 117 is more critical than seal 119 as coolantleaked from seal 119 will simply re-enter the coolant reservoir.

Support members 111 can take any of a variety of forms, a few of whichare shown in the cross-sectional views of FIGS. 2-6. The support membershown in FIG. 2 is comprised of a plurality of spokes 201 that rigidlycouple feed tube 109 to shaft 103. The support member shown in FIG. 3also includes a plurality of spokes 301, however in this support memberthe spokes are coupled to a pair of concentric rings 303 and 305 whichare rigidly coupled to feed tube 109 and shaft 103, respectively.Although the members shown in FIGS. 2 and 3 both utilize spokes, themember shown in FIG. 3 is generally easier to fabricate than the membershown in FIG. 2. It will be appreciated that a fewer or a greater numberof spokes can be used with either of the support members shown in FIGS.2 and 3.

FIG. 4 shows another alternate embodiment of the support member. Inparticular, member 401 is a ring-shaped member which includes aplurality of perforations 403 that provide the necessary coolant path.Member 401 can utilize fewer or greater numbers of perforations,different size perforations or perforations of varying size within asingle member.

FIG. 5 shows another alternate embodiment of the support member. Asshown, member 501 includes a plurality of slotted openings 503.Preferably openings 503 are angled, thus allowing members 501 to providean additional means for pumping the coolant as it passes through theregion between feed tube 109 and shaft 103. Although member 501 is shownwith slanted slots, it should be understood that other shapes can beused in the slanted openings, for example slanted perforations.Additionally, member 501 can utilize fewer or greater numbers ofopenings than shown.

In addition to using a plurality of support members to couple feed tube109 to shaft 103, in at least one embodiment of the invention acontinuous support member 601 is used, as illustrated in FIG. 6. Asshown, member 601 is comprised of a continuous support strut whichhelically wraps around feed tube 109 and couples it to shaft 103. Due tothe helical shape of member 601, coolant is actively pumped in theregion separating feed tube 109 from shaft 103, thus insuring continuouscoolant flow to the rotor assembly.

In order to improve coolant flow when the coolant undergoes thedirectional change at the end of feed tube 109, adjacent to end 105 offeed tube 103, preferably the inside surface 701 of the end of feed tube103 is shaped, for example as illustrated in FIG. 7. Shaping surface 701promotes coolant flow and reduces flow stagnation. It will beappreciated that shaping surface 701 aids coolant flow regardless of theconfiguration used for the support member.

It should be understood that an electric motor utilizing the rotorassembly cooling system of the present invention is not limited to aspecific implementation. FIG. 8 conceptually illustrates the basicelements of an electric motor utilizing the present invention. It willbe appreciated that FIG. 8, as with the other figures included herein,is not drawn to scale.

The other elements of electric motor 800 are the same as in aconventional electric motor. For example, motor 800 includes a stator801, drive shaft bearings 803 and motor case 805. The rotor coolingassembly, in addition to the other elements previously described indetail, also includes a coolant reservoir 807 within a housing 809 and acoolant pump 811. In at least one embodiment, housing 809 also containsthe transmission thus allowing the coolant to also be used to cool andlubricate the transmission. In at least one alternate embodiment,housing 809 is a separate housing used only for coolant containment andcirculation, thus requiring the other end of the drive shaft to becoupled to the power train of the vehicle. It will be appreciated thatthe rotor cooling assembly of the invention can be used in conjunctionwith other cooling systems, for example a coolant system integrated intothe motor housing.

As will be understood by those familiar with the art, the presentinvention may be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof. Accordingly, thedisclosures and descriptions herein are intended to be illustrative, butnot limiting, of the scope of the invention which is set forth in thefollowing claims.

1. An electric motor comprising: a stator; a rotor mounted within said stator, said rotor comprised of a shaft, wherein a portion of said shaft is hollow; a coolant feed tube rigidly attached to said shaft and mounted within said hollow portion of said shaft, wherein a separation between an outer surface of said coolant feed tube and an inner surface of said hollow portion of said shaft defines a coolant flow region; and means for pumping coolant into said coolant feed tube, wherein said coolant flows through said coolant feed tube in a first direction and flows through said coolant flow region in a second direction.
 2. The electric motor of claim 1, said shaft further comprising an open first end and a closed second end, wherein said coolant feed tube passes through said open first end of said shaft, and wherein an inner surface of said closed second end reverses said coolant flow from said first direction to said second direction.
 3. An electric motor cooling system comprising: a rotor shaft, said rotor shaft comprised of an open end, a closed end and a hollow portion between said open end and said closed end; a coolant feed tube positioned within said hollow portion of said rotor shaft, wherein a separation between an outer surface of said coolant feed tube and an inner surface of said hollow portion of said shaft defines a coolant flow region; means for rigidly coupling said coolant feed tube to said rotor shaft; and means for pumping coolant through a closed coolant circuit, said closed coolant circuit comprised of said coolant flowing in a first direction through said coolant feed tube, said coolant reversing direction at said closed end of said rotor shaft, and said coolant flowing in a second direction through said coolant flow region.
 4. The electric motor cooling system of claim 3, wherein said pumping means is comprised of a coolant pump.
 5. The electric motor cooling system of claim 3, wherein said means for rigidly coupling said coolant feed tube to said rotor shaft further comprises a plurality of support members.
 6. The electric motor cooling system of claim 5, wherein each of said plurality of support members is comprised of a plurality of spokes.
 7. The electric motor cooling system of claim 5, wherein each of said plurality of support members is comprised of a first ring proximate to and attached to said outer surface of said coolant feed tube, a second ring proximate to and attached to said inner surface of said hollow portion of said shaft, and a plurality of spokes rigidly coupling said first ring to said second ring.
 8. The electric motor cooling system of claim 5, wherein each of said plurality of support members is comprised of a ring, wherein an inner edge of said ring is proximate to and attached to said outer surface of said coolant feed tube and wherein an outer edge of said ring is proximate to and attached to said inner surface of said hollow portion of said shaft, and wherein said ring is further comprised of a plurality of holes passing from a first side of said ring to a second side of said ring.
 9. The electric motor cooling system of claim 8, wherein each of said plurality of holes is angled.
 10. The electric motor cooling system of claim 5, wherein each of said plurality of support members is comprised of a ring, wherein an inner edge of said ring is proximate to and attached to said outer surface of said coolant feed tube and wherein an outer edge of said ring is proximate to and attached to said inner surface of said hollow portion of said shaft, and wherein said ring is further comprised of a plurality of slots passing from a first side of said ring to a second side of said ring.
 11. The electric motor cooling system of claim 10, wherein each of said plurality of slots is angled.
 12. The electric motor cooling system of claim 3, wherein said means for rigidly coupling said coolant feed tube to said rotor shaft further comprises a continuous support strut, said continuous support strut helically wrapped around and attached to said coolant feed tube, wherein an outer edge of said continuous support strut is proximate to and attached to said inner surface of said hollow portion of said shaft.
 13. The electric motor cooling system of claim 3, wherein an inner surface of said closed end of said rotor shaft is shaped.
 14. The electric motor cooling system of claim 3, wherein an inner surface of said closed end of said rotor shaft has a non-planar shape to promote said coolant reversing direction at said closed end of said rotor shaft.
 15. A method of cooling an electric motor in an electric vehicle, said method comprising of the steps of: rotating a rotor shaft of the electric motor at a shaft rotation rate; rotating a coolant feed tube mounted within a hollow portion of said rotor shaft at a tube rotation rate, wherein said tube rotation rate is equivalent to said shaft rotation rate; pumping a coolant in a first direction through said coolant feed tube; and flowing said coolant in a second direction through a coolant flow region between an outer surface of said coolant feed tube and an inner surface of said hollow portion of said rotor shaft.
 16. The method of claim 15, wherein said first direction is opposite said second direction.
 17. The method of claim 15, further comprising the step of rigidly attaching said coolant feed tube to said hollow portion of said rotor shaft with a plurality of support members.
 18. The method of claim 15, further comprising the step of rigidly attaching said coolant feed tube to said hollow portion of said rotor shaft with a continuous support strut helically wrapped around said coolant feed tube.
 19. The method of claim 15, further comprising the step of redirecting said coolant from said first direction to said second direction, said redirecting step further comprising the step of pumping said coolant against an inner surface of a closed end of said rotor shaft. 